Clocking Cars: What timing belts and silicon timing have in common

Automotive technology has made significant advances since the 1970s in terms of safety, reliability, performance and fuel efficiency. While advances in engine technology, vehicle emissions, and safety features dominate the headlines, there is a considerable amount of innovation happening under the hood.

One area often overlooked involves the timing components used to deliver critical clocks within electrical control units (ECU) for Advanced Drivers Assistance Systems (ADAS), vehicle networking, infotainment and various other sub-systems of the car.

Modern automobiles use anywhere from 20 to 70 standalone timing devices, and this number is growing as cars adopt more advanced technology with every generation. And surprisingly, advances in automotive timing technology share a lot in common with a key component used in every internal combustion engine – the timing belt.

The traditional approach for providing automotive timing is to use quartz-based crystals or oscillators (XO). Quartz timing solutions are akin to timing belts in internal combustion engines. Timing belts synchronize the rotation of the crankshaft and camshafts to open and close the engine’s valves with high precision. Similarly, quartz timing devices are used to synchronize various electronic components within ECUs. Both solutions are relatively simple, cost-effective and straightforward.

Over the past five years, there has been a significant increase in function and complexity integrated into ECU designs, which is increasing the amount of semiconductor electronics within a vehicle. While crystals and XOs have been popular in cars with reduced electronic content, new solutions are now required. One of the biggest drawbacks to a quartz device is that it is highly susceptible to shock and vibration failure, often making them the component in an automotive electronic design with the highest failure in time (FIT) rate by a wide margin.

The risk of higher vehicle maintenance and ownership costs increases as more quartz timing devices are adopted in new designs. In comparison, timing belts were broadly used in the 1970s and 1980s because they were light, inexpensive and operated quietly.  However, timing belts, like quartz XOs, suffered from reliability issues. As advances in engine technology progressed, it became apparent a better solution was required. Since 2000, the automotive industry has largely migrated to timing chains, which provide significantly better durability and reliability than timing belts. 

 Table 1 summarizes the similarities between timing belts/chains and automotive timing solutions.

 

Timing belts/timing chains

Automotive clock generators

Synchronizes the rotation of the crankshaft and camshaft to open and close the engine’s valves with high precision 

 

Synchronizes various networking and autonomous driving functions

Precision required to time each cylinder’s intake and exhaust strokes and maximize fuel efficiency and transmit rotational power synchronously

Frequency precision and low jitter critical.  Signal tuning possible to meet emissions requirements. 

Can be used to drive multiple camshafts, in addition to water pumps and oil pumps

 

Can be used to drive processors, FPGA, GPUs, etc.

Timing belts popular in the 80s.  Light, inexpensive, operate quietly. 

Oscillators and crystals popular in cars with less electronic content.  Electrification of cars driving need to minimize cost and complexity.  Unified clock solution improves system reliability by replacing multiple potential points of failure.

Timing chains being adopted now. Much more durable and reliable than timing belts.

 

Automotive clocks being adopted now, replacing XOs and crystals.  Automotive clocks provide additional performance and reliability features not supported by quartz solutions

Table 1.  Timing belt/chain and automotive timing comparison

 

Low risk transition to silicon is underway 

Electrification of vehicles has increased semiconductor content within an automobile to more than $1,000 and is expected to continue growing. Automotive designers are challenged with the task of adopting more complex solutions while improving system-level reliability. Similar to the migration from timing belts to timing chains, recent advancements in timing technology are now available that enable a low-risk transition from quartz devices to silicon solutions to improve overall system reliability.

Crystals and XOs are simple devices that provide a single clock output. If they fail to start up or oscillate, it impacts the operation of the processor it is driving. Further, crystals and oscillators have no monitoring capability to notify the system of a potential problem in advance. Given the sheer number of timing signals required by ADAS, autonomous driving, in-vehicle Ethernet networking, and other ECUs, it is imperative the industry adopt a new paradigm for automotive timing.

 Silicon-based automotive clock generators are now available that provide a mix of different frequencies, enabling a single IC to replace up to 12 crystals and XOs. While the trend to replace multiple quartz devices with a silicon solution has been broadly adopted in communications and industrial applications for more than 15 years, the majority of automotive designs predominantly use quartz today.

The latest clock generators are now AEC-Q100 qualified and offer advanced features that solve challenges unique to automotive applications, finally enabling a low-risk transition from quartz. These devices not only unify frequency synthesis into a single device, they provide reliability features that crystals and XOs can’t support.  Table 2 summarizes these unique value-added features and benefits.

 

Feature

Benefit

Input reference health monitoring

Actively monitors input reference frequency versus nominal rate and declares alarm if user-defined threshold exceeded

Complementary LVCMOS drivers

Balanced differential signal routing minimizes emissions

Clock redundancy

If primary reference fails, clock device switches to internal reference

Spread Spectrum (SSC)

Ability to turn SSC on to reduce EMI

Output enable/disable

Disable unused outputs to minimize power consumption

Frequency selection

Change output frequency on one or more outputs via simple pin selection

Signal format translation

Signal format configurable on a per-output basis (LVCMOS, HCSL, LVDS, LVPECL)

On-chip power regulation

Simplifies PCB layout, ensures reliable low jitter clock synthesis in noisy system environments

In-system programmability

Simple device reconfigurability via I2C serial interface

 Table 2.  Automotive Clock Key Benefits

 

Tenfold improvement in quality 

Similar to the emergence of timing belts close to 50 years ago, silicon timing solutions can help the industry evolve further, as electronics become more pervasive in automotive applications. Silicon-based automotive clock generators reduce multiple potential points of failure by consolidating multiple frequency references into a single device.  The latest silicon timing solutions actively monitor system clocks and generate early warning indicators to notify the system to take action before the performance of the application further deteriorates.

Clock redundancy enables the device to switch to a secondary clock in the event the primary reference clock fails, ensuring highly reliable operation.   Clock monitoring and clock redundancy are new capabilities of automotive clocks that enable ECU-based sub-systems to operate in a smarter, more efficient way while optimizing system-level reliability.  Multiple automotive features that drivers interact with every day will stand to benefit from using these smart timing solutions. 

Electromagnetic interference (EMI) and emissions are key concerns in automotive applications which must pass stringent CISPR requirements.  Clocks are of special significance because, without special precautions, clocks distributed across a PCB can generate radiated emissions.  Single-ended clocks are especially prone to radiated emissions. To mitigate this effect, new automotive clocks are now available that support complementary LVCMOS signaling.  This technique provides a load balanced differential signal with matching rise/fall times and amplitudes that is highly effective at mitigating EMI, providing a simplified solution to passing CISPR requirements with margin.

Compared to crystal-based timing ICs, migrating to unified, silicon-based timing ICs enables ADAS, in-vehicle networking, infotainment, and other sub-systems in cars to perform at overall higher quality levels. As the industry accelerates the transition from quartz devices to silicon timing solutions, automotive customers can expect to see a tenfold improvement in overall quality related to timing components.

James Wilson is General Manager, Timing Products, at Silicon Labs.